Heavy teen marijuana use may cut life short by 60

Heavy marijuana use in the late teen years puts men at a higher risk for death by age 60, a new long-term study suggests.

Swedish researchers analyzed the records of more than 45,000 men beginning in 1969 and 1970. The scientists from the Karolinska Institutet in Stockholm reported that 4,000 died during the 42-year follow-up period, and men who'd used marijuana heavily at ages 18 and 19 were 40 percent more likely to die by age 60 compared to guys who hadn't used the drug.

The authors of the new study, published in the American Journal of Psychiatry, said the findings contradict previous research involving the same group of men.

But this study was longer and participants might have reached an age where the long-term effects of cannabis were taking a toll on health, said addiction expert Scott Krakower, an assistant unit chief of psychiatry at Zucker Hillside Hospital, in New Hyde Park, NY.

"Cannabis users have poorer health in general. You'd expect there to be increased mortality risk," Krakower told CBS News. He pointed to another long-term study linking early heavy marijuana use with lung cancer, and a second study that associates the drug with increased heart problems.

"Marijuana users generally may have poorer diets and they might be tobacco smokers. There's an increased linkage between weed and tobacco," said Krakower.

Dr. Kevin Hill, a member of the American Psychiatric Association's Council on Addiction Psychiatry, told CBS News, "One of the key messages from a study like this comes down to two words: dose matters."

The study looked at teenagers who had used marijuana more than 50 times.

Hill, an assistant professor of psychiatry at McLean Hospital and Harvard Medical School, said most people who use marijuana don't use it at heavy levels. "Nine percent of adults use it at that level and develop an addiction."

He said the study is limited because it didn't provide specifics about heavy use and continued use.

Using marijuana earlier in life is linked to poorer psychological health, he said, and that can contribute to more health problems down the road.

"It is well-established that if you begin using at an early age and use a lot then, there are significant negative outcomes particularly in terms of mental health and it wouldn't be a surprise for that to translate to long-term health problems," Hill said.

Earlier cannabis use is linked to cognitive problems. Hills said, "One 2012 study showed early, regular use of marijuana - the kind of level they describe in this study -- led to an eight point decline in IQ over time."

He said it's also associated with worse anxiety and depression, adding, "If you start using marijuana at an early age, you're more likely to express a psychotic disorder."

In this day and age of continued debate over marijuana policy issues, Hill said, "This kind of study is incredibly important. We don't have definitive answers, but it underscores if you are using heavily, you're probably going to have some negative consequences."